Method for device for detecting low-contrast and high-contrast defects in transparent or translucent objects

Abstract

The invention concerns an optical inspection method for the line inspection of transparent or translucent objects ( 2 ) travelling at fast rate between a light source ( 3 ) and means ( 4 ) to take images of the objects and to analyze the images taken, so as to detect defects in the objects. According to the invention, the method consists of: controlling the single light source ( 3 ) so that said source successively produces two types of illumination for each object travelling in front of said source, the first type being homogeneous illumination whilst the second type is formed of alternate dark areas (s) and light areas (c) with discontinuous spatial variability, taking images of each travelling object when each thereof is successively illuminated by both types of lighting, and analyzing the images taken with the first and second types of illumination, with a view to detecting high contrast defects and low contrast defects respectively

1 . Optical inspection method for the line inspection of transparent or translucent objects ( 2 ) travelling at fast rate between a light source ( 3 ) and means ( 4 ) to take images of the objects and to analyze the images taken, so as to detect defects in the objects, characterized in that it consists of:
 controlling the single light source ( 3 ) so that said source successively produces two types of illumination for each object travelling in front of said source, the first type being homogeneous illumination whilst the second type is formed of alternate dark areas (s) and light areas (c) with discontinuous spatial variability,   taking images of each travelling object when each thereof is successively illuminated by both types of lighting,   and analyzing the images taken with the first and second types of illumination, with a view to detecting high contrast defects and low contrast defects respectively.   
     
     
         2 . Method according to  claim 1 , characterized in that it consists of controlling the light source ( 3 ) so that the second type of illumination is formed of alternate dark areas and light areas with discontinuous spatial variability occurring in a periodic cycle, whether or not of constant value. 
     
     
         3 . Method according to  claim 1 , characterized in that it consists of controlling the light source ( 3 ) so that the second type of illumination with discontinuous spatial variability, and for each cycle, comprises:
 a phase (P H ) maintaining, over a nonzero length (L H ), a high level of light intensity (I H ) at a substantially constant value,   a phase (P B ) maintaining, over a nonzero length (L B ), a low level light intensity (I B ) at a substantially constant value,   and transition phases (P HB , P BH ) between the high and low levels of light intensity with respective lengths (L HB , L BH ).   
     
     
         4 . Method according to  claim 3 , characterized in that it consists of controlling the light source ( 3 ) so that the lengths (L HB , L BH ) of the transition phases (P HB , P BH ) tend towards zero duration. 
     
     
         5 . Method according to  claim 3 , characterized in that it consists of controlling the light source ( 3 ) so that the high level of light intensity (I H ) is at least greater than the low level of light intensity (I B ) with the high level of light intensity (I H ) being at least sufficient to pass through the objects ( 2 ), whilst the low level of light intensity (I B ) tends towards a zero value. 
     
     
         6 . Method according to  claim 3 , characterized in that it consists of controlling the light source ( 3 ) so that the high (and respectively low) levels of light intensity of the light areas (c) (and respectively dark areas (s)) have separate values for different cycles. 
     
     
         7 . Device for the optical line inspection of transparent or translucent objects ( 2 ) travelling at fast rate between a light source ( 3 ) and means ( 4 ) to take images of the objects and to analyze the images taken, so as to detect defects in the objects, characterized in that it comprises:
 means ( 9 ) to control the single light source ( 3 ) so that said light source successively produces two types of illumination when each object travels between the light source ( 3 ) and the image taking and analysis means ( 4 ), the first type being homogenous illumination whilst the second type is lighting formed of alternate dark areas (s) and light areas (c) with discontinuous spatial variability,   and means ( 4 ) to take images of each object illuminated by both types of illumination and to process the images taken with the first and second type of illumination, with a view to detecting high contrast defects and low contrast defects respectively.   
     
     
         8 . Inspection device according to  claim 7 , characterized in that the light source ( 3 ) consists of a series of elementary sources ( 11 ) grouped into adjacent zones (Z) independently controlled with respect to light intensity and/or illumination time, a light guide ( 13 ) being arranged in front of each zone so as to obtain light of homogeneous intensity at the output of each guide. 
     
     
         9 . Inspection device according to  claim 8 , characterized in that each light guide ( 13 ) is formed of a parallelepiped of transparent material. 
     
     
         10 . Inspection device according to  claim 8 , characterized in that each light guide ( 13 ) is formed by a channel delimited by walls of which at least some separate the light guides from each other. 
     
     
         11 . Inspection device according to  claim 8 , characterized in that at least one diffuser ( 15 ) is inserted on the pathway of the light emitted by the elementary sources. 
     
     
         12 . Inspection device according to  claim 7 , characterized in that the light source ( 3 ) is formed of a uniform light source in front of which a liquid crystal display is placed that is controlled so as to make determined areas opaque or transparent. 
     
     
         13 . Inspection device according to  claim 7 , characterized in that the light source ( 3 ) consists of a system projecting images onto a capture screen, which correspond either to a homogeneous light-coloured image or to an image comprising alternate dark areas and light areas with discontinuous spatial variability. 
     
     
         14 . Inspection device according to  claim 7 , characterized in that the light source ( 3 ) consists of a series of organic light-emitting diodes grouped into adjacent zones (Z) independently controlled with respect to light intensity and/or illumination time. 
     
     
         15 . Inspection device according to  claim 8 , characterized in that a screen controlled electrically to assume either a transparent state or a diffusing state is arranged on the pathway of the light of the light source. 
     
     
         16 . Inspection device according to  claim 7 , characterized in that the light source ( 3 ) consists of elementary sources grouped into zones controlled independently with respect to light intensity and/or illumination time, a screen controlled electrically to assume either a transparent state or a diffusing state being arranged on the light path. 
     
     
         17 . Inspection device according to  claim 7 , characterized in that it comprises a linear or circular polarizing filter in front of the light source, and a linear or circular filter in front of the image taking means.